Mumbai: The number of women being trafficked from Bangladesh into Mumbai brothels is rising as part of greater migration from India`s eastern neighbour, and police and social groups need to do more to rescue and repatriate them, a charity said on Thursday.

The number of Bengali-speaking commercial sex workers in the city`s main red-light district of Kamathipura is at a record high, according to data compiled by Prerana, a non-profit focused on trafficking and sex workers.

The total includes some women from the eastern state of West Bengal.

"The increased numbers dovetail with increased migration from Bangladesh, and migrants are particularly vulnerable to traffickers," said Priti Patkar, co-founder of Prerana.

"They`re so desperate, they are easily lured by the promise of a job or a better life," she told the Thomson Reuters Foundation.

Of the 213 children of sex workers enrolled at Prerana`s night care centre in Kamathipura from 2010-15, 128 had a Bengali-speaking mother, the data showed. Similar increases have been seen in other parts of the city, Patkar said.

There were about a dozen each from the states of Uttar Pradesh, Maharashtra, Karnataka and Andhra Pradesh.

There are more than 3 million people of Bangladeshi origin in India, according to official data. Hundreds arrive undocumented every day, often crossing the 4,000 km (2,500 mile)border with a trafficker or "agent" who preys on poor, rural communities with promises of good jobs and a better life.

Rising migration within Asia is putting growing numbers of migrants at risk of being trafficked and abused by human smuggling networks, the United Nations Office for Drugs and Crime (UNODC) said in a report last year on the criminal trade, which is worth $2 billion a year in Asia.

South Asia is the fastest-growing region for human trafficking in the world, and the second-largest after Southeast Asia, according to the UNODC.

More than 150,000 people are known to be trafficked within South Asia every year, but the trade is underground and the real number is likely to be much higher. The numbers are expected to rise as migration within Asia grows.

Trafficked Bangladeshi women in Mumbai are often too afraid and ignorant of their rights to seek help, Patkar said. They are also reluctant to bring charges against their traffickers after being rescued from the brothels.

India signed an agreement with Bangladesh last year to strengthen cooperation and information sharing and ensure speedier investigations and prosecutions of traffickers.

The agreement has made it easier to rescue and repatriate victims of trafficking, some of whom were previously treated as illegal immigrants.

"Now, there is a clear process: we take their deposition, then hand them over to an NGO there, which takes responsibility for their rehabilitation," a Mumbai police spokesman said. "This is a better outcome for the women."

This week, for the first time, a Bangladeshi trafficker was convicted on the strength of the victim`s testimony given over a video link from Dhaka, where she had been repatriated after her rescue from a brothel in Mumbai. Activists and lawyers say such depositions could help curb trafficking.